Lenses for use in light-emitting diode (LED) devices are mass manufactured by mechanical forming such as injection molding. Although prior art lenses are molded using thermoplastic resins such as acrylic resins and polycarbonate resins, the currently increasing power of LED devices invites the problem that thermoplastic resins' heat resistance and discoloration resistance are short.
Also, lead-free solders are often used nowadays. Since the lead-free solders have a higher melting temperature than conventional solders, optical devices are usually soldered to substrates while heating at a temperature of 260° C. or higher. When soldering at such high temperature, lenses of prior art thermoplastic resins can no longer be used because the lenses will deform or yellow due to the heat.
Under the circumstances, a number of studies have been made on the use of silicone resins in the lenses associated with LED or the like. When lenses are manufactured from silicone resins by forming techniques such as injection molding, mold release agents are directly applied to the metal mold by spraying or the like to provide for smooth release from the metal mold. The step of spraying the mold release agent is not so desirable in view of productivity. In addition, the surface of molded parts is altered by the transfer of the mold release agent to the molded parts. This is one of factors that detract from transparency.
The references pertinent to the present invention include JP-A 2000-231002 corresponding to U.S. Pat. No. 6,285,513, JP-A 2000-17176, and JP-A 2004-221308.